Over last few weeks my veins seem more prominent and blue all over body. why. i'm worried i may have a disease?

Probably normal.: Veins can enlarge and shrink for many reasons most commonly levels of hydration, genetics, aging, sun exposure, temperature changes and even skin color being more prominent in fair skinned people. Most commonly what you are experiencing is a normal variation but you probably should see a vein specialist for a full venous evaluation so that they could examine you and answer all of your questions.

Prominent veins: It is likely not related to anything serious. Prominent veins that are not tender, red, or bulging are probably not caused by an underlying disease. Varicose veins are dilated veins, usually on the lower legs, that are due to incompetent valves within the walls of the veins and causes irregular appearance of the veins. If that's what you are seeing then try wearing compression stockings.